Test module for motor control center subunit

ABSTRACT

A system and method are provided for coordinating the installation and removal a motor control center subunit with the power connection and interruption thereof A system of interlocks and indicators causes an operator to install a motor control center subunit into a motor control center, and connect supply and control power thereto, in a particular order. Once installed, a test module system included with the subunit provides for pass-through connection of signals from equipment test points. The test module can thus relay internal conditions of the subunit to the operator without a need for disengaging or opening the subunit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. provisionalapplication Ser. No. 60/891,831, filed on Feb. 27, 2007, the disclosureof which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to a system and method for motorcontrol, and more particularly, to a test module for use with a subunitfor a motor control center. The test module provides equipmentconnection points and voltage test points, so that a user can monitorinternal conditions of the subunit when the subunit is installed intothe motor control center. In one embodiment, the system and methoddescribed herein provide for connection of external accessories, such asmotor meggaring devices, voltage/current testing equipment, and motorwellness units, to internal test points of the subunit, without a needfor removing or opening the motor control center subunit.

A motor control center is a multi-compartment steel enclosure with a bussystem to distribute electrical power, on a common bus system, to aplurality of individual motor control units mountable within thecompartments. The individual motor control center subunits are commonlyreferred to as “buckets” and are typically constructed to be removable,pull-out units that have, or are installed behind, individual sealeddoors on the motor control center enclosure. These buckets may containvarious motor control and motor protection components such as motorcontrollers, starters, contactor assemblies, overload relays, circuitbreakers, motor circuit protectors, various disconnects, and similardevices for electric motors. The buckets connect to the supply powerlines of the motor control center and conduct supply power to the lineside of the motor control devices, for operation of motors. Motorcontrol centers are most often used in factories and industrialfacilities which utilize high power electrical motors, pumps, and otherloads.

Typically, when installing or removing motor control center buckets, thepower supply lines are connected. To remove such a bucket, a deadfrontdoor of the bucket or of the motor control center is opened and anoperator manually pulls on the bucket to separate the primarydisconnects, or “stabs,” from the bus system, thereby disconnecting thepower supply. Installation of a bucket is accomplished in a similarmanner, wherein the operator manually pushes the bucket into acompartment of the motor control center to engage the bucket stabs withthe bus system, thus connecting the system to supply power. The lineconnections or stabs may be difficult to maneuver manually when anoperator is supporting the entire bucket or when the stabs are notvisible.

Attempts have been made to improve upon the manual installation anddisconnection of motor control center buckets and supply powerconnections from live supply power lines, risers, and/or a vertical busof a motor control center. Other systems have employed pivotable handlesinside the buckets to pivot line connectors to and from supply lines.However, many of these systems require that the bucket or compartmentdoor be open to manipulate the handles and line stabs.

Similarly, once a bucket has been fully installed and/or sealed in placein a motor control center, it becomes difficult to monitor conditionsinside the bucket without disconnecting the bucket and removing it fromthe motor control center. For example, in some systems, to test line orload voltages and currents, contactor or starter voltages and currents,and control signals, doors or seals of the bucket would need to beopened, or the bucket would be partially or completely removed.

It would therefore be desirable to design a motor control center bucketassembly that overcomes the aforementioned drawbacks. Thus, it would bedesirable to provide for remote connection or disconnection of the linestabs of a bucket to the power supply lines or bus of a motor controlcenter from a distance. In the event of an arc or arc flash, any heatedgas, flame, and/or the arc itself should preferably be contained behindthe bucket compartment door or “deadfront.” It would further bedesirable to include a test module which could convey conditions insidea fully installed bucket to an operator via an interface on an externalside of the bucket.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a system and method for installing amotor control center subunit or bucket into a motor control center andelectrically connecting motor control components of the bucket to apower supply. The system and method utilize moveable line stabs toengage the power supply (such as a series of bus bars) after the buckethas been secured in the motor control center, in order to containpotential arc flashes. An arrangement of interlocks coordinates theconnection of supply power with installation and removal of the bucket.A test module is disposed within the bucket and provides for indicationof bucket operation characteristics after full installation of the motorcontrol center subunit into the motor control center.

Therefore, in accordance with one aspect of the present invention, amotor control center subunit includes a housing and a base moduledisposed within the housing for through-door electrical connectivity andconfigured to relay at least one internal electrical condition of thesubunit. The motor control center subunit also includes at least onebase module accessory removably connectable to the base module andconfigured to receive at least one internal electrical condition of thesubunit. The base module is configured to allow a user to determine atleast one internal condition of the subunit to the accessory.

In accordance with another aspect of the invention, a motor controlcenter includes a motor control center frame having at least onecompartment and a motor control center subunit constructed to seat inthe at least one compartment of the motor control center frame. Themotor control center also includes an actuating mechanism attached tothe motor control center subunit to control movement of a plurality ofconductive line contacts and a subunit tester configured to relay acondition of the conductive line contacts outside the subunit to a user.

According to a further aspect of the invention, a method ofmanufacturing a base module for a motor control center includes thesteps of constructing a motor control center subunit to seat within amotor control center and constructing a front panel for the motorcontrol center subunit. The method also includes the steps of disposinga base module within the front panel and attaching test point connectorsbetween the base module and at least one internal component of the motorcontrol center subunit to convey signals indicative of operationconditions of the motor control center subunit.

Various other features and advantages of the present invention will bemade apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a partial perspective view of a number of motor control centersubunits installed in a motor control center.

FIG. 2 is a perspective view of a motor control center subunit of FIG.1, removed from the motor control center.

FIG. 3 is a top view of the motor control center subunit of FIG. 1showing a number of stabs in a retracted position.

FIG. 4 is top view of the motor control center subunit of FIG. 3 showingthe stabs in a test position.

FIG. 5 is a top view of the motor control center subunit of FIG. 4showing the stabs in an extended position.

FIG. 6 is a cross-sectional view of the motor control center subunit ofFIG. 3 taken along line 6-6 of FIG. 3.

FIG. 7 is a cross-sectional view of the motor control center subunit ofFIG. 5 taken along line 7-7 of FIG. 5.

FIG. 8 is a detailed view of a portion of the motor control centersubunit of FIG. 6 showing an arc shield, line contact, and supplyconductor thereof.

FIG. 9 is a detailed view of a portion of the motor control centersubunit of FIG. 7 showing a line contact and supply conductor thereof.

FIG. 10 is a plan view of a control handle of one embodiment of thepresent invention.

FIG. 11 is a side view of the control handle of FIG. 9.

FIG. 12 is a plan view showing the control handle of FIG. 9 rotatedninety degrees.

FIG. 13 is a side view of the control handle of FIG. 11.

FIG. 14 is a side view showing the control handle of FIG. 11 depressedinto a motor control center subunit.

FIG. 15 is a plan view showing the control handle of FIG. 11 rotatedninety degrees.

FIG. 16 is side view of the control handle of FIG. 14.

FIG. 17 is a bottom view of the motor control center subunit of FIG. 3.

FIG. 18 is a bottom view of the motor control center subunit of FIG. 5.

FIG. 19 is a perspective view of a test point connection.

FIG. 20 is a rear perspective view of the motor control center subunitof FIG. 2.

FIG. 21 is a front view of the motor control center subunit of FIG. 3.

FIG. 22 is a front view of the motor control center subunit of FIG. 4.

FIG. 23 is a front view of the motor control center subunit of FIG. 5.

FIG. 24 is a front perspective view of a base module assembly.

FIG. 25 is a front perspective view of the base module assembly of FIG.24 with an attached accessory and cover.

FIG. 26 is a rear perspective view of an integrated voltage test pointaccessory and base module.

FIG. 27 is a front perspective view of the integrated voltage test pointaccessory and base module of FIG. 26.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description makes reference to supply power, supply powerlines, motor power, load power, line power, and the like. It isappreciated that such terms may refer to a variety of both common anduniquely conditioned voltage and current characteristics, including butnot limited to, three phase AC power, single phase AC power, DC power,multiple DC power lines, or any combination thereof. Such powercharacteristics will be generally referred to as being provided on abus, supply line, or riser of a motor control center. However, it isappreciated that the present invention may find applicability in otherpower connectivity configurations, adapted or apart from motor controlcenters. An example of supply power commonly used in motor controlcenters is 480V three-phase AC power distributed over three separatesupply bus bars. In addition, references to “motor control components”shall be understood to include the various types of devices and controlcomponents which may be housed in a motor control center bucket forconnection to the supply power. Such devices and components includecontactors, relays, motor controllers, disconnects, circuit protectivedevices, and the like.

Referring to FIG. 1, a partial perspective view of a motor controlcenter structure 10 is shown. As discussed above, motor control centersare generally formed of a frame 314 that may include compartments orenclosures for multiple control modules or buckets 11, 13, 14, 15, 16,17. Bucket 16 is shown fully installed into motor control centercompartment or enclosure 12 such that its front panel 18 is seatedsecurely against the periphery of enclosure 12 and flush with the frontpanel 20 of bucket 14. In this regard, bucket 16 includes a number oflatching mechanisms 22 on front panel 18 so that an operator may lockbucket 16 into place once installed. In some embodiments, front panel 18may be a deadfront door having a set of hinges 19 in order to permitaccess to motor control components within bucket 16 while bucket 16 isinstalled in enclosure 12 of motor control center 10. However, even whenclosed or sealed, front panel or door 18 still permits access to circuitbreaker assembly 28, stab indicator 24, shutter indicator 26, and linecontact actuator 31. Line contact actuator 31 is a mechanism forengaging line contacts (FIG. 2) with line power from the motor controlcenter 10. Thus, even when bucket 16 is fully installed in enclosure 12and latches 22 have been secured, an operator may still use disconnecthandle 30 and may open slide 32 to insert crank 34 to move one or moreline contacts (not shown) of the bucket 16. When slide 31 is moved asideto permit access to actuating mechanism 31, door 18 is prevented fromopening, thereby closing off access to components inside bucket 16.Additionally, a user may desire to padlock the slide 31 in the closedposition, to further regulate who may operate actuating mechanism 31 andwhen.

In other embodiments, a crank 300 for actuating an actuating assembly302 may include a flange 304 which abuts a front door 306 of a bucket 13when the crank 300 is connected to the actuating assembly 302 thereof.Because the flange 304 extends further than the actuating assembly 302and overlaps front door 306, flange 304 acts as an interlock to preventdoor 306 from opening when the crank 300 is connected for operation ofactuating assembly 302.

As an alternative to, or in combination with, using a hand crank, amotor drive 308 may be used to operate an actuating assembly 310 of abucket 17. Such a motor drive 308 may be connected permanently orremovably to actuating assembly 310. Preferably, motor drive 308 is a DCmotor remotely operable from distances of 10-50 ft, whether wirelesslyor with a wired controller. Motor drive 308 may be powered by a batteryor by an electrical connection with motor control center 10, such as viathe control power contact 44 shown in FIG. 2 or a similar plug orconnection. It is recognized, however, that many other types, sizes, andconfigurations of motor drive 308 are equivalently applicable. Forexample, it may be desirable to connect a motor drive 312 inside abucket, as shown with bucket 11. In addition, an interlock circuit maybe included (not shown) to only allow operation of the motor drive 308,312 when the bucket 11, 17 is installed in motor control center 10. Thismay be as simple as a contact switch that completes an input powercircuit or may include more sophisticated position sensors or latchsensors.

A base module assembly 400 is also provided on front panel 18, to allowfor attachment of various testing accessories (FIGS. 24-27) while bucket16 is installed in the enclosure 12 of the motor control center 10 andfront panel 18 is sealed. That is, base module assembly 400 may beconfigured as an electrical pass-through to convey voltages and currentsfrom internal test points of the bucket 16 to access points on frontpanel 18. Alternatively, base module assembly 400 may be connected toconvey signals which are merely indicative of internal conditions of thebucket 16, such as internal line and load voltages and currents,component temperatures, control voltages and currents, componentconditions, and the like. These signals may be data signals which areprocessed to determine internal conditions, or may be scaled versions ofthe internal voltages or currents themselves. While shown as beinglocated on a front surface of front panel 18, it is also envisioned thatbase module assembly 400 can also be positioned on a rear surface offront panel 18 to allow for additional ease in the diagnosis andtroubleshooting of electrical issues in motor control center 10 or fixedpermanently to motor control components (not shown) within bucket 16 andnot on the front panel. When base module assembly 400 is fixedpermanently within bucket 16 and not on front panel 18, a hole is cut inthe front panel such that base module assembly 400 is accessibletherethrough. When base module 400 is positioned on a front surface offront panel 18 (as shown in FIG. 1) and is not in use, it is envisionedthat base module 400 be covered by a metal arc flash resistant cover(not shown) and locked with an appropriate locking mechanism, thusreducing chances of an arc flash and allowing access to base module 400only by qualified personnel.

Referring now to FIG. 2, a perspective view of a motor control centerbucket 16 is shown. It is noted that bucket 16 may have a housing thatincludes a number of panels surrounding bucket 16 to fully or partiallyenclose the components thereof. As shown, bucket 16 includes a pair ofside panels 52 and a front panel 18, which support motor control devicesand internal bucket components. An upper panel and a rear panel havebeen removed to show the internal components of bucket 16. Front panel18 is configured to fit snugly and securely within a motor controlcenter such that a rim 38 of the front panel 18 seats against the innerperiphery (not shown) of a motor control center enclosure. For purposesof dust protection, rim 38 may optionally include a compressible orflexible seal, such as a rubber seal, or other gasket-type component.Once bucket 16 is inserted into a motor control center enclosure, latchmechanisms 22 may be turned with a key, a screwdriver, or by hand sothat latch arms 40 abut an inner surface of the outer periphery (notshown) of an enclosure to hold bucket 16 in place and/or prevent bucket16 from being removed. Similarly, an automatic retention latch 60 isshown in an engaged position. Upon advancement of line contacts or stabs46, 48, 50 automatic retention latch 60 is triggered to engage a frameor divider pan (FIG. 7) that segregates upper and lower compartments ofthe motor control center unit in which bucket 16 is installed.

When slide 32 of line contact actuator 31 is moved aside, an opening 36is exposed. Opening 36 preferably has a unique configuration to accept aspecialized crank 34 (as shown in FIG. 1). Additionally, when slide 32is moved aside as shown, slide 32 extends over a portion of front panel18. Thus, in embodiments in which front panel 18 is a hinged door,moving slide 32 to expose opening 36 will inhibit a user from openingfront panel 18. Accordingly, so long as an operator has a crank insertedinto opening 36 of actuator 31, the operator cannot open the door of thebucket 16.

Bucket 16 also includes a number of conductive contacts or stabs 44, 46,48, 50. Control power contact 44 is preferably fixedly attached to therear of bucket 16, whereas supply power stabs 46, 48, 50 are moveablewith respect to bucket 16. However, it is appreciated that control powercontact 44 may also be moveable in a similar manner to line power stabs46, 48, 50. Control power contact 44 is of a suitable construction toconduct a control power (typically a few volts) to motor controlcomponents (not shown) disposed within bucket 16. In embodiments wherecontrol power contact 44 is permanently positioned at the rear of bucket16, control power contact 44 will engage a control power supply line orbus upon installation of bucket 16 into a motor control center.

Supply power stabs 46, 48, 50, on the other hand, do not initiallyengage supply power lines or buses when bucket 16 is installed into amotor control center. Rather, stabs 46, 48, 50 are initially inretracted position 42, disposed inside bucket 16. One skilled in the artwill appreciate that a number of configurations of supply power stabs46, 48, 50 may be utilized. In the embodiment shown, stabs 46, 48, 50are shaped to grasp about a supply line, bus, or riser of the motorcontrol center 10 of FIG. 1.

The stab assembly 58, in addition to stabs 46, 48, 50, also includes astab bracket 59 to which the stabs 46, 48, 50 are attached. Stab bracket59 holds stabs 46, 48, 50 in an orientation for subsequent engagementwith the supply power lines or buses of motor control center 10 ofFIG. 1. It is recognized, however, that stab assembly 58 of FIG. 2 mayinclude any number of configurations, such as for independently moveablestabs, for other than three stabs, or for actuation by other than ashaft, as will be described below. A shutter or isolator assembly 54 isdisposed in the rear of bucket 16, between stab assembly 58 and theexterior of bucket 16. Isolator assembly 54 includes a number ofmoveable shutters 56 which operate to either expose or isolate the stabs46, 48, 50 from the power lines or buses of the motor control center 10of FIG. 1.

FIG. 3 depicts a top view of bucket 16, with all housing panels removedexcept for front panel or door 18. As shown, stab assembly 58 haspositioned stabs 46, 48, 50 in a retracted position 42 wherein the stabs46, 48, 50 are located inside bucket 16. Accordingly, shutters 56 ofshutter assembly 54 are closed, isolating the stabs 46, 48, 50 from thesupply power bus or line of a motor control center such as shown inFIG. 1. As shown in FIG. 3, each shutter 56 includes two separateshielding members 62 and 64, 66 and 68, 70 and 72. The shutter 56 forstab 46 includes a left shielding portion 62 and a right shieldingportion 64, each being angled toward stab 46. Likewise the shutters 56for stabs 48 and 50 include left shielding portions 66, 70 and rightshielding portions 68, 72 respectively, each being angled toward thecorresponding stab. However, the shutter 56 for stab 50 includes anadditional mechanical connection 74. That is, a shutter arm 74 isprovided to control a shutter indicating mechanism 76 which displays toan operator via front panel indicator 26 whether the shutters 56 areopen or closed, as will be described in further detail below. Similarly,a cam or bell crank 80 is attached via rod 78 to stab assembly 58 totranslate movement of the stab to a microswitch 82. Microswitch 82operates to turn on and off the supply of control power from controlpower contact 44 to motor control components, such as contactors oroverload relays (not shown), of bucket 16.

Referring now to FIG. 4, the bucket 16 is shown having the stab assembly58 in a test position 43. Stabs 46, 48, and 50 have been advanced to apoint or test position 43 at which they nearly touch or just touchshutters 56, but shutters 56 are still closed. Since shutters 56 areclosed, stabs 46, 48, 50 are isolated from supply power buses, thuspreventing arcs from occurring between stabs 46, 48, 50 and the buses.Being in the test position, stab bracket 59 is moved forward such thatactuating shaft or drive 84 is visible. Preferably, shaft 84 is a rotarydrive shaft and is connected to the socket of opening 36 shown in FIG. 2for operation via crank 34, shown in FIG. 1. Referring back to FIG. 4,during the advancement of stab assembly 58, automatic latch 60 has beentriggered to engage the enclosure of the motor control center into whichbucket 16 has been installed. Also due to the advancement of stabassembly 58, rod 78 is pulled by stab bracket 59 such that cam 80 hasrotated away from microswitch 82. Microswitch 82 is thus actuated topermit control voltage from the control power contact 44 to a motorcontrol component, such as a contactor or overload relay (not shown). Itis appreciated, however, that microswitch 82, cam 80 and rod 78 areoptional. In other words, embodiments of the present invention maysimply permit control voltage to pass through control power contact 44directly to motor control components immediately upon installation ofbucket 16 into a motor control center when contact 44 engages a controlpower bus.

FIG. 5 depicts another top view of the bucket 16 wherein the stabs 46,48, 50 are in an extended/engaged position 45. In operation, stabs 46,48, 50 are advanced or extended from the test position 43 of FIG. 4towards shutters 56 and impinge upon angled portions 62-72 of theshutters 56. As the stabs 46, 48, 50 are forced forward into and againstthe surfaces of shutters 56, the stabs 46, 48, 50 separate the leftangled portions 62, 66, 70 and right angled portions 64, 68, 72 of theshutters 56 to expose the stabs 46, 48, 50 to supply power buses 88, 90,92, respectively. Preferably, a biasing or closure force is provided tobias the right angled portions 64, 68 72 and the left angled portions62, 66, 70 towards one another, so that the shutters 56 automaticallyclose upon retraction of stabs 46, 48, 50. It is recognized thatnumerous other ways of opening and closing shutters 56 are possible andcontemplated. For example, rather than employing two shutter portionsfor each shutter, one shutter portion having one beveled surface couldbe slid aside by the advancement of the stabs. Or, the shutters could beconnected for manipulation by the turning of rotary shaft 84. Thus, theshutters 56 could comprise one or several sliding panels with or withoutbeveled surfaces. In other words, shutters 56 may be operated to openand close by the movement of the stabs, by the movement of the stabassembly, by the turning of the actuating shaft, by other actuatingcomponents, or by a manual control. Regardless, once the stabs 46, 48,50 have penetrated through shutters 56, the stabs 46, 48, 50 may beadvanced or extended to engage power supply bus bars 88, 90, 92.

Also shown in FIG. 5 is a second microswitch 94 connected to activateand deactivate circuit breaker 30. When stabs 46, 48, 50 reach the fullyengaged position 45 with bus bars 88, 90, 92, stab bracket 59 of stabassembly 58 actuates microswitch 94. When actuated, microswitch 94permits closure of circuit breaker 30, completing the circuit betweenbus bars 88, 90, 92 and the line side of motor control components (notshown) in bucket 16. Otherwise, microswitch 94 prevents closure ofcircuit breaker 30.

For removal of bucket 16, circuit breaker 30 is opened, disconnectingsupply power to the motor control devices (not shown) of bucket 16.Stabs 46, 48, 50 may then be retracted from bus bars 88, 90, 92 by areverse motion of rotary shaft 84. Once stabs 46, 48, 50 pass shutters56, the right and left portions 62-72 thereof will automatically closetogether to isolate the stabs from bus bars 88, 90, 92. Preferably, theshutter portions 62-72 and all or some of the housing panels, includingfront panel 18 and a rear panel (not shown), of bucket 16 are formed ofplastic or another insulating material. After stabs 46, 48, 50 have beenfully retracted, automatic latch 60 will release from engagement withthe motor control center, and an operator may then slide bucket 16 outof the motor control center.

Referring now to FIG. 6, a cross-sectional view of bucket 16 taken alongline 6-6 of FIG. 3 is shown. The left angled portion 66 of a shutter 56is shown isolating the central stab 48, since stab 48 is in theretracted position 42 of FIG. 3. In FIG. 6, it can be seen that stabassembly 58 holds stab 48 in position and engages rotary shaft 84, shownin section. Therefore, FIG. 6 illustrates the moving components used toactuate a stab 48. An operator may use a ratchet or crank (not shown)through opening 36 of slide 32 to turn rotary shaft or worm gear 84. Astab guide 96 includes a thread bearing 100 to transform the rotationalmotion of rotary shaft 84 into a translational motion of stab assembly58. Thus, rotary shaft 84 and stab guide 96 may generally be referred toas a racking-type actuating mechanism for extending and retracting thestabs 46, 48, 50, relative to bucket 16. As stab assembly 58 is rackedor otherwise advanced towards the extended or engaged position 45 shownin FIG. 5 (i.e. a motion to the left, as oriented in FIG. 6) stab 48will impinge upon shutters 66.

FIG. 6 also illustrates the operation of a number of interlocks whichcoordinate installation of the bucket 16 with connection of supplypower. That is, based upon the motion of the stab assembly 58, aretention latch 60 is triggered to retain bucket 16 in its installedposition inside the motor control center frame 314, followed by acircuit breaker interlock 316 being moved to permit an operator to closecircuit breaker handle 30 (FIG. 1). When stab assembly 58 is advanced, asloped lip 104 of stab assembly 58 will strike a bottom portion 106 ofautomatic retention latch 60. As sloped lip 104 follows the advancingmotion of the stab assembly 58, it will rotate retention latch 60 intoan upward position wherein bottom portion 106 rests on stab guide 96 andlatch 60 extends through a groove 98 of a divider pan 380 of the motorcontrol center frame (FIG. 1) to retain bucket 16 therein. Additionally,in the embodiment shown, a circuit breaker interlock 316 mechanicallyprevents an operator from closing a circuit breaker 28 (FIG. 1) whenstab assembly 58 is in the retracted position 42. This mechanicalembodiment of circuit breaker interlock 316 may be used in addition to,or as an alternative to, the microswitch embodiment shown in FIG. 5. Asshown in FIG. 6, circuit breaker interlock 316 has a downward-slopingend 320 and an upward-sloping end 318. The downward-sloping end 320 ofcircuit breaker interlock 316 acts as a stop, preventing plate 322 fromshifting. Plate 322 is interconnected with circuit breaker handle 30(FIG. 1), so that circuit breaker handle 30 cannot be turned unlessplate 322 shifts.

FIG. 7 is another cross-sectional view, showing the same portion ofbucket 16 as is shown in FIG. 6. However, FIG. 7 is a cross-sectiontaken along line 7-7 of FIG. 5, thus showing component locations whenthe stab assembly 58 is in the extended position 45. Stab assembly 58has been advanced by the turning of worm gear 84 such that stab 48 hasseparated and pushed past shutters 66. As the stab assembly 58 wasadvanced, sloped lip 104 of stab assembly 58 lifted bottom portion 106of retention latch 60, such that retention latch 60 now engages adivider pan 380 through opening 98. Divider pan 380 is connected to themotor control center frame (FIG. 1) to separate two bucket compartmentsthereof. Thereafter, as the stab assembly 58 reached its fully extendedposition 45, the stab guide 96 abutted the upward-sloped end 318 ofcircuit breaker interlock 316, drawing circuit breaker interlock 316away from plate 322. Thus, downward-sloped end 320 of circuit breakerinterlock 316 no longer blocks shifting of plate 322 when stab assembly58 is in the extended/engaged position 45. In other words, installationand power connection are coordinated in that a user cannot remove thebucket 16 from the motor control center once the automatic retentionlatch is triggered, and can only turn the circuit breaker handle 30(FIG. 1) when the stab assembly reaches its extended position 45.

FIG. 8 is an enlarged view of the stab 48 and shutter 66 area of thecross-sectional view of FIG. 6. Conductive stab 48 is coupled to aflexible conductor 130, such as a cable, via a coupling portion 132 ofstab assembly 58. Flexible conductor 130 is of a construction suitableto conduct supply power, via stab 48, to the line side of a motorcontrol component (not shown). As shown in FIG. 9, when stab 48 and stabassembly 58 are racked or otherwise advanced forward to an extendedposition 45, flexible conductor 130 flexes to maintain electricalconnectivity with stab 48 via coupler 132. Accordingly, the motion ofstab 48 relative to bucket 16 does not interfere with the connectivityof the stab 48 with a motor control component.

Referring now to FIGS. 10-16, an alternative stab actuating feature isshown. A manually drivable handle 116 may replace or be used incombination with the crank 34, the crank 300, the motor drive 308, orthe motor drive 312 of FIG. 1 and the racking mechanism of FIG. 6. Insuch embodiments, the rotary shaft or worm gear 84 depicted in previousembodiments may be replaced with a non-tapped shaft or rod directlyconnected to stab assembly 58. FIG. 10 shows such a handle 116 in alocked, starting position 118 that corresponds to the stabs disengagedposition 42 of FIG. 3. As shown in FIG. 11, handle 116 is separated andbiased from front panel 18 of a bucket by a spring 120 and extendsthrough stab actuating opening 36. By rotating handle 116 ninetydegrees, as shown in FIGS. 12 and 13, handle 116 may be unlocked 122. Insome embodiments, an interlock system may be included to preventunlocking of handle 116 until bucket 16 is fully installed into a motorcontrol center. Such an interlock may be incorporated into the shaft 84of handle 116. Once unlocked, handle 116 may be driven or depressedtowards front panel 16, compressing spring 120, as shown in FIG. 14. Thedepressed position 124 of handle 116 corresponds to the stabs engagedposition of FIG. 5. Handle 116 may then be rotated another ninetydegrees 126, as shown in FIGS. 15 and 16, to lock the handle in thestabs engaged position 124, against the force of spring 120. Fordisengagement of the stabs, handle 116 is rotated to unlockedorientation 122, pulled outward to the stab disengaged position 42 andturned ninety degrees to a locked position 118. In a general sense,therefore, embodiments of the present invention may include variousconfigurations of simplified, manual actuation of the stabs, similar tothat shown in FIGS. 10-16.

Referring now to FIG. 17, a bottom view of the bucket 16 of FIG. 3 isshown, wherein the stab assembly 58 and stabs 46, 48, 50 are in aretracted position 42. In retracted position 42, shutters 56 of shutterassembly 54 are closed, isolating or shielding stabs 46, 48, 50 insidebucket 16. Control power stab 44, on the other hand, is un-shielded andwill be connected to a control power once bucket 16 is installed into amotor control center. However, microswitch 82 is in an activated state,due to the pressure thereon by cam 80. When microswitch 82 is in theactivated state, as shown, microswitch 82 is interrupting control powerfrom contact 44. Thus, the motor control components (not shown) housedin bucket 16 cannot initially be operated. Cam 80 will be moved by rod78 via advancement of stab bracket 59, deactivating microswitch 82 andthereby permitting the flow of control power to motor control components(not shown) of the bucket 16. Cam 80 also acts to display a locationstatus of the stabs 46, 48, 50 to an operator. As will be discussedbelow, cam 80 has a number of colors printed thereon which are displayedthrough front door 18 of bucket 16 via stab indicator 24 (FIG. 1).

In the embodiment shown, circuit breaker interlock 316 includesmicroswitch 94, which gates the operation of circuit breaker 30. FIG. 17shows microswitch 94 in a deactivated state, in which button 334 thereofis not depressed. Arm 330 of microswitch 94 is positioned to abut aledge 332 of circuit breaker interlock 316 Thus, when circuit breakerinterlock 316 moves, due to the motion of stab assembly 58, the arm 330of microswitch 94 will pivot, depressing button 334. When button 334 isdepressed, microswitch 94 will be activated and will electrically enableoperation of circuit breaker 28 (FIG. 1).

Also shown in FIG. 17 is a shutter arm 336, having a sloped end 338. Asstab 46 is advanced, stab 46 will engage the sloped end 338 and slidepast shutter arm 336, thereby shifting shutter arm 336 to the left, asdepicted in FIG. 17. When shutter arm 336 is shifted, it will strike atab 340 of rod 76. As will be further described below, when tab 340 isstruck, rod 76 will rotate, changing the color showing on shutterindicator 26 through door 18 of bucket 16.

FIG. 18 is a bottom view of the bucket 16 of FIG. 5, illustrating thelocation of components thereof when the stab assembly 58 is in theextended/engaged position 45. When stab assembly 58 was advanced, rod 78caused cam 80 to rotate, releasing pressure on microswitch 82. Thus,microswitch 82 is shown in a deactivated state, permitting the flow ofcontrol power from control power contact 44 to motor control components(not shown) of bucket 16. Additionally, the advancement of stab assembly58 moved circuit breaker interlock 316 such that ledge 332 thereof drewarm 330 of microswitch 94 to an activated position. That is, arm 330 ofmicroswitch 94 is depressing button 334 to enable operation of circuitbreaker 30, now that stabs 46, 48, 50 are in the engaged position 45.

As discussed above, the advancement of stabs 46, 48, 50 to the extendedposition 45 separates a number of shutter portions, including shutterportion 62. In the embodiment shown in FIG. 18, the advancement of stab46 also caused a shift in shutter arm 336. That is, stab 46 impingedupon sloped end 338 of shutter arm 336 and drove shutter arm 336 to theleft, as depicted in FIG. 18, as stab 46 advanced. When shutter arm 336shifted due to the motion of stab 46, shutter arm 336 struck a tab 340(FIG. 17) of rod 76, rotating rod 76 and altering the color of shutterindicator 26.

Also shown in FIG. 18 are test point connections 444, which areconnected from the base module assembly 400 on a front panel 18 of themotor control center 10 to various connection points within the bucket11. It is contemplated that the internal connection points or voltagetest points of the test point connections 444 may include locations oncontrol power contact 44, stab assembly 58, shutter assembly 54, circuitbreaker assembly 28, short circuit protection devices (not shown),starters and other internal control components(not shown), and otherlocations of interest within the motor control center 10.

A detailed perspective view of a test point connection 444 is shown inFIG. 19. Test point connection 444 comprises a wire connection orprimary wire 402, which interfaces with a voltage point in the bucket11, and a voltage sensor 446. The voltage sensor 446 comprises a voltagesensing wire 412 that reads out to an accessory (FIGS. 25-27). Voltagesensing wire 412 is preferably soldered to a spring clip 406, which isconstructed of an easy-to-solder-to metal and sized to match thediameter of the primary wire 402. It is recognized, however, that manyways exist to attach voltage sensing wire 412. Spring clip 406 assembleswith primary wire 402 using tabs 404 that slide over the end of theprimary wire 402. Once released, tabs 404 spring tight and hold thevoltage sensor 446 in place with the primary wire 402. After voltagesensor 446 is installed on the primary wire 402, an insulator, such aselectrical tape 408 for example, is wrapped around the primary wire 402and spring clip 406 for dielectric insulation. Preferably, test pointconnection 444 is insulated to an extent that additional fingerprotection may not be needed. It is recognized, however, that anydesired level of insulation may be incorporated into test pointconnection 444.

Optionally, a temperature sensor, such as a thermocouple 410, may beplaced on the voltage sensor 446 and secured with electrical tape 408 orvia other connecting/insulating techniques. In this regard, it isrecognized that any number of voltage sensing wires 412 andthermocouples 410 may be then bundled together to be connected to theback side 416 of an accumulation module or base module assembly 400.Similarly, it will be appreciated that thermocouple 410 and voltagesensor 446 may be selected to minimize interference with the signals ofprimary wire 402.

Referring now to FIG. 20 a partial interior perspective view of a motorcontrol center bucket 16 is shown. For purposes of illustration, severalcomponents are not shown, including side panels, a top panel, a stabguide, and a circuit breaker assembly. Therefore, circuit breaker handle30 is visible through front door 18 of bucket 16. As shown, handle 30 isattached via a shaft 344 to a fin 346. Though not shown, a circuitbreaker assembly is also attached to be actuated by shaft 344.

Circuit breaker interlock 316 is shown in an alternate configuration,having an upward-sloping end 350 near door 18 and a pair of verticaltines 352 and one horizontal tine 354 at an opposite end. Vertical tines352 are engaged by a stab guide 96 (FIG. 7) when the stabs of bucket 16are advanced. Horizontal tine 354 engages a spring (not shown) to biasthe circuit breaker interlock 316 toward door 18 until the stabs ofbucket 16 are advanced. Until the circuit breaker interlock 316 is slidaway from door 18 by advancement of the stabs, upward-sloping end 350 ofcircuit breaker interlock 316 is inserted into an opening 356 ofinterlock plate 322. Because upward-sloping end 350 is inserted intoopening 356, interlock plate 322 is prevented from shiftingside-to-side, until circuit breaker interlock 316 is pulled away fromdoor 18 by the advancement of the stabs of bucket 16.

Interlock plate 322 has a projection 362 extending therefrom to fin 346of circuit breaker handle 30. Projection 362 is integrally formed with,or affixed to, plate 322, and is configured to move side-to-side withplate 322, when upward-sloping end 350 of circuit breaker interlock 316is not inserted in opening 356. Projection 362 has a pair of tines 348which extend outwardly therefrom, on either side of fin 346. Therefore,when plate 322 is prevented from moving, tines 348 prevent fin 346 fromrotating, thereby preventing an operator from turning circuit breakerhandle 30. In this manner, circuit breaker interlock 316 prevents a userfrom closing circuit breaker handle 30 until the stabs of bucket 16 arefully extended. It is understood that circuit breaker interlock 316,interlock plate 322, and associated components may have a number ofshapes, orientations, and configurations which allow for thefunctionality described herein.

When an operator closes circuit breaker handle 30, fin 346 impinges uponthe tines 348 of projection 362 in a counter-clockwise direction. Theforce of fin 346 on tines 348 causes projection 362 and interlock plate322 to shift to the left, as orientated in FIG. 20. When plate 322shifts left, it obscures opening 36 of actuating assembly 31 (FIG. 1),obstructing access to worm gear 84. So long as circuit breaker handle 30is closed, fin 346 will prevent plate 322 from moving back to the right,as shown in FIG. 20. In other words, fin 346 of circuit breaker handle30 effectively prevents a user from moving the stabs of bucket 16 whilethe circuit breaker is closed and supply power is conducting. Oncecircuit breaker handle 30 is opened again, fin 346 will not press ontines 348, plate 322 will be permitted to shift back to the positionshown in FIG. 20, and an operator will again have access to worm gear84. When the operator reverses worm gear 84 to withdraw the stabs,circuit breaker interlock 316 will be biased back toward plate 322,preventing plate 322 from sliding, and thus preventing circuit breakerhandle 30 from turning.

Also shown in FIG. 20 is cam 80 and rod 78. As discussed above withrespect to FIGS. 3 and 4, rod 78 is connected to translate movement ofthe stabs of bucket 16 to a rotational motion of cam 80. Cam 80 servestwo purposes: to activate and deactivate microswitch 82, as describedabove, and to control the stab location status shown on stab indicator24. Therefore, cam 80 has a number of colors printed on its edge.Visible in FIG. 20 are a red edge section 360 and a yellow edge section358. A green edge section (not shown) is currently being presented atstab indicator 24, to indicate the stabs retracted position 42 of FIG.3. Yellow edge section 358 will be presented at stab indicator 24 whenthe stabs have left the retracted position and are advanced towards thetest position 43 of FIG. 4. Red edge section 360 will be presented atstab indicator 24 when the stabs have reached the extended/engagedposition 45 of FIG. 5.

Similarly, rod 76 of shutter indicator 26 (FIG. 4) is connected to awheel 362, which presents a number of colors at shutter indicator 26, toindicate the status of the shutter assembly 54 (FIG. 3). That is, asdescribed with respect to FIG. 18, the movement of stab assembly 58causes a rotation in rod 76. As depicted in FIG. 20, rod 76 is affixedto wheel 364 such that a rotation of rod 76 causes wheel 364 to turn.

FIG. 20 also shows the back side 416 of the base module assembly 400 asit is integrated with the front panel 18 of the bucket 16. In oneembodiment of the current invention, internal test point connectionports 418 for both voltage sensing wires 412 and thermocouples 410 arearranged on the back side 416 of the base module 400. In otherembodiments, the back side 416 of base module 400 may includeconnections for only one or for several voltage sensing wires 412 oronly one or several thermocouples 410. Although internal test pointconnection ports 418 have been described for voltage and temperaturesensing applications, it is contemplated that internal test pointconnection ports 418 may be provided to accumulate and output other datafrom the bucket 16, such as insulation characteristics, motor wellnesscharacteristics, and other characteristics of operation.

Referring now to FIGS. 21-23, the status indicating features of stabindicator 24 and shutter indicator 26 are shown. That is, FIGS. 21, 22,and 23 are a front view of the bucket 16 shown in FIGS. 3, 4, and 5,respectively. With respect to FIG. 21, a user has moved slide 32 ofactuating assembly 31 to the right, exposing opening 36. In alternativeembodiments, a user may need to unlock a cover or padlock (not shown)which restrict movement of or access to the slide 32. As shown, slide 32overlaps door 18, preventing a user from opening door 18 while opening36 is exposed. Shutter indicator 26 is displaying a green “shuttersclosed” status 368, since the shutters 56 are closed due to the stabsretracted position 42 of FIG. 3. Therefore, FIG. 21 also shows stabindicator 24 displaying a green “stabs retracted” status, correspondingto the stabs retracted position 42 of FIG. 3. FIG. 22 also shows thegreen “shutters closed” status 368 on shutter indicator 24, but shows ayellow “test position” status on the stab indicator 24, corresponding tothe test position 43 of FIG. 4.

FIG. 23 shows a front view of bucket 16 when the stabs are in theextended/engaged position 45 of FIG. 5. Therefore, shutter indicator 26now displays a red “shutters open” status 370, since the stabs 46, 48,50 have separated the shutters 56 (FIG. 5), and the stab indicator 24 ofFIG. 23 shows a red “stabs engaged” status 360. Circuit breaker handle30 has been turned, closing the circuit breaker 31 and permitting theflow of supply power to motor control components inside bucket 16. Asdescribed above with respect to FIG. 20, turning circuit breaker handle30 when the stabs are engaged causes interlock plate 322 to be shiftedby movement of circuit breaker fin 346. Accordingly, FIG. 23 illustratesthat actuating assembly opening 36 is now obscured by interlock plate322. It is understood that further measures, such as padlocking a coverover actuating mechanism 31 and slide 32, may also be made to furtherrestrict access to the actuating mechanism 31 when the bucket 16 isconnected to supply power.

Referring now to FIG. 24, the front side 420 of a base module 400 isshown. Mounting holes 422 are located at the corners of the base module400. In the current embodiment, fasteners (not shown) are used toremovably mount base module 400 to the door 18 of a control module 11,however, it is contemplated that other permanent or removable mountingmeans may be used to attach base module 400 to a bucket 11. Alsodisposed in base module assembly 400 are internal test point connectionports or pass-through connection ports 418, which form an interfacebetween an accessory 432 and locations of interest within the motorcontrol center 10. Alignment holes 428 and accessory snap lock holes 426are provided to position and secure an accessory 432 to the base module400.

Referring now to FIG. 25, an indicator accessory 432 is shown interfacedwith base module assembly 400 via snap lock tabs 434. As shown,indicator accessory 432 is provided with illuminated indicators 436 fordisplaying operating conditions of the motor control center 10 as wellas internal characteristics of the accessory 432. For example, anindicator 436 may display a blown fuse signal, a low battery signal, oran indication that the accessory 432 is or is not properly connected tothe base module 400. Further, indicator 436 may display informationregarding connections within the motor control center 10 or bucket 11including the load side of a short circuit protection device within thebucket 11, the load side of a starter, control power, bucket ground, andthe like. It is also envisioned that indicator 436 comprise a 3 LEDarrangement for indicating presence of a 480 VAC voltage and thatindicator accessory 432 be used in association with “test before touch”and “live-dead-live” testing practices when accessing motor controlcenters.

In addition to using a simple indicator 436 as an accessory, it iscontemplated that more advanced accessories 432 may also be included.For example, accessory 432 may also be a motor megger unit, a motorwellness unit, or other diagnostic devices.

As known in the art, moisture, contamination, and heat can combine tobreak down motor winding insulation, shorten motor life, and possiblyresult in motor failure. A motor megger or mega-ohm meter is anautomatic insulation resistance tester that monitors insulationcharacteristics within the motor. Operating as a circuit tester, themotor megger puts high voltage at a low current across two conductors toensure the conductors are properly insulated. Thus, in embodiments inwhich accessory 432 is a motor megger unit, internal test connections ofthe system may be attached at terminal connects (not shown) positionedon a back surface of the motor megger.

Motor wellness characteristics refers to the wellness of contactors andmotor starters and other components within the motor. Contactors aregenerally used in motor starter applications to switch on/off a load aswell as to protect a load, such as a motor, or other electrical devicesfrom current overloading. As such, a typical contactor has three contactassemblies—a contact assembly for each phase or pole of a three-phaseelectrical device. Each contact assembly, in turn, includes a pair ofstationary contacts and a pair of moveable contacts. One stationarycontact will be a line side contact and the other stationary contactwill be a load side contact. The moveable contacts are controlled by anactuating assembly comprising a contact carrier and an armature magnetassembly which is energized by a coil to move the moveable contacts toform a bridge between the stationary contacts. When the moveablecontacts are engaged with both stationary contacts, current is allowedto travel from the power source or line to the load or electricaldevice. When the moveable contact is separated from the stationarycontacts, an open circuit is created and the line and load areelectrically isolated from one another.

Despite their relative durability, all contactors have a finite useablelife. Component wear, contact surface erosion, friction, jam, contactwelding, arc-generated debris, and other factors limit the length oftime and/or number of operations through which a contactor may be used.Since contactors and motor starters are important components of bothautomation and control systems, monitoring their remaining useable life,or “wellness,” to predict impending faults before occurrence isessential. A motor wellness module monitors performance of suchcomponents by measuring various currents and voltages in one or both ofa switched line and an actuating coil to determine indications ofimpending faults of the device. Accordingly, it is recognized that theinternal test point connections provided at base module 400 may beadapted for use with a particular accessory 432. Alternatively, the testpoint connections may be universal, in which case an accessory 432 maybe configured to interface with only those connection ports 418.

Referring now to FIGS. 26-27, another embodiment of base module 400 andaccessory 448 is shown, where accessory 448 is permanently integratedwith base module 400. In this embodiment, accessory 448 is a voltagetest point accessory having a front surface 442 with accessoryconnection holes 438 within which a user can insert test probes (notshown). Accessory connection holes 438 are access points for testing ofvarious internal voltage readings such as bucket ground, load side ofthe short circuit protection device, load side of a starter, and bucketcontrol power. The access points 438 are covered by a shutter system 440to prevent accidental contact with bucket components. Although voltagetest point accessory 448 is shown in FIGS. 26 and 27 as an integratedaccessory, the voltage test point accessory 448 may also be configuredto be detachable from the base module 400 as shown with respect toaccessory 432. Furthermore, although accessory 448 is shown in FIG. 28as having only accessory connection holes 438, it is contemplated thatthe accessory 448 may include any combination of connection holes 438and illuminated indicators 436 (FIG. 25).

Thus, an interlock system and a through-door testing system have beendisclosed, in a number of embodiments. The interlock system coordinatesthe installation and power connections of a motor control center subunitor bucket. When a user slides the bucket completely into the enclosureof a motor control center, the line contacts or stabs of the bucket areshielded from the bus bars. Once the bucket is inserted into theenclosure, the front door of the bucket must be closed and the circuitbreaker must be off/open in order for the operator to have access to thestab actuating mechanism. Additionally, a user may have to unlock apadlock and latch to gain access to the slide and/or actuatingmechanism. Once the actuating mechanism opening is exposed, a crank (ormotor drive) may be connected thereto. The stab indicator will show agreen “stabs-disengaged” status, and the shutter indicator will show agreen “shutters-closed” status. As the stabs are initially advanced, anautomatic retention latch is triggered to engage the frame of the motorcontrol center and prevent removal of the bucket therefrom. Also, amicro-switch is activated by the initial advancement of the stabs,turning on control power for the motor control components inside thebucket. When the line stabs reach the back of the bucket, but have notmoved past the shielding shutters, the bucket is in the “test” position.The stab indicator will show a yellow “test” status, and the shutterindicator will still show a green “shutters-closed” status. When thestabs are advanced further, they will open the shutters, causing theshutter indicator to show a red “shutters-open” status. When theshutters reach and engage the bus bars, the stab indicator will show ared “stabs-engaged” status and the circuit breaker interlock will betripped. At this point, the circuit breaker will be permitted to closeonce the user removes the crank or motor from the actuating mechanism.When a user closes the circuit breaker, access to the actuatingmechanism will be obscured by a circuit breaker interlock plate. Thecircuit breaker handle and/or the actuating mechanism slide can bepadlocked in place at this point to maintain the engaged, operatingstate now achieved.

When the interlock system has fully installed the bucket, thethrough-door connectivity system still allows a user to detect ormonitor the internal conditions of the bucket. Moreover, it isunderstood that the interlock system thus disclosed also coordinates thepower disconnection and removal of the bucket from the motor controlcenter, by reverse operation of the aforementioned interlocks andindicators.

While the above base module assembly 400 has been described for use witha motor control center, it is also envisioned that base module assembly400 be implemented for use with systems that house motor controlarrangements that include a motor starter and a free-standing, enclosedpanel. Additionally, base module assembly 400 can be implemented for usewith combination starters which enclose a breaker/disconnect-fuse and amotor starter.

Accordingly, one embodiment of the present invention includes a motorcontrol center subunit includes a housing and a base module disposedwithin the housing for through-door electrical connectivity andconfigured to relay at least one internal electrical condition of thesubunit. The motor control center subunit also includes at least onebase module accessory removably connectable to the base module andconfigured to receive at least one internal electrical condition of thesubunit. The base module is configured to allow a user to determine atleast one internal condition of the subunit to the accessory.

In accordance with another embodiment of present invention, a motorcontrol center includes a motor control center frame having at least onecompartment and a motor control center subunit constructed to seat inthe at least one compartment of the motor control center frame. Themotor control center also includes an actuating mechanism attached tothe motor control center subunit to control movement of a plurality ofconductive line contacts and a subunit tester configured to relay acondition of the conductive line contacts outside the subunit to a user.

In another embodiment of the present invention, a method ofmanufacturing a base module for a motor control center includes thesteps of constructing a motor control center subunit to seat within amotor control center and constructing a front panel for the motorcontrol center subunit. The method also includes the steps of disposinga base module within the front panel and attaching test point connectorsbetween the base module and at least one internal component of the motorcontrol center subunit to convey signals indicative of operationconditions of the motor control center subunit.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A motor control center subunit comprising: a housing; a base moduledisposed within the housing for through-door electrical connectivity andconfigured to relay at least one internal electrical condition of thesubunit; at least one base module accessory removably connectable to thebase module and configured to receive at least one internal electricalcondition of the subunit; and wherein the base module is configured toallow a user to determine at least one internal condition of the subunitto the accessory.
 2. The motor control center subunit of claim 1 furthercomprising a plurality of selectively moveable conductive contactsdisposed within the housing.
 3. The motor control center subunit ofclaim 2 wherein the conductive contacts are moveable when the housing isseated in a motor control center and a front panel of the housing is ina closed position.
 4. The motor control center subunit of claim 1wherein the base module accessory is configured to test at least one ofan internal current and a motor winding insulation.
 5. The motor controlcenter subunit of claim 1 wherein the internal electrical condition ofthe subunit is sensed by a test point connector.
 6. The motor controlcenter subunit of claim 1 wherein the base module accessory is a motorwellness indicator.
 7. The motor control center subunit of claim 1further comprising a hinged cover attached to the base module andconfigured to enclose the accessory.
 8. The motor control center subunitof claim 7 wherein the hinged cover is clear and the accessory is anindicator.
 9. The motor control center subunit of claim 1 furthercomprising wired connections that connect the base module to circuitrylocated within the motor control center subunit.
 10. The motor controlcenter subunit of claim 9 wherein the wired connections are configuredto connect to at least one of a line side of a short circuit protectiondevice, a load side of a short circuit protection device, a load side ofa starter, a phase current, and a handle mechanism.
 11. A motor controlcenter comprising: a motor control center frame having at least onecompartment; a motor control center subunit constructed to seat in theat least one compartment of the motor control center frame; an actuatingmechanism attached to the motor control center subunit to controlmovement of a plurality of conductive line contacts; and a subunittester configured to relay a condition of the conductive line contactsoutside the subunit to a user.
 12. The motor control center of claim 11further comprising a plurality of selectively moveable conductive linecontacts disposed within the subunit.
 13. The motor control center ofclaim 12 wherein the conductive line contacts are moveable when thesubunit is seated in a motor control center and a front panel of thesubunit is in a closed position.
 14. The motor control center of claim11 wherein the subunit tester is configured to test at least one of aninternal current and an internal voltage.
 15. The motor control centerof claim 11 wherein the subunit tester comprises a test module and anaccessory, the accessory comprising one of a motor megger, a motorwellness indicator, and a voltage tester.
 16. The motor control centerof claim 11 further comprising a hinged cover attached to the testmodule and configured to enclose the subunit tester, wherein the hingedcover is non-opaque and the accessory is an indicator.
 17. The motorcontrol center of claim 11 further comprising electrical connectionsbetween the test module and a number of test points of internal motorcontrol center subunit components, and wherein the electricalconnections are configured to be substantially non-interfering withconditions at the number of test points connect to at least one of aline side of a short circuit protection device, a load side of a shortcircuit protection device, a load side of a starter, a phase current,and a handle mechanism.
 18. A method of manufacturing a base module fora motor control center comprising: constructing a motor control centersubunit to seat within a motor control center; constructing a frontpanel for the motor control center subunit; disposing a base modulewithin the front panel; and attaching test point connectors between thebase module and at least one internal component of the motor controlcenter subunit to convey signals indicative of operation conditions ofthe motor control center subunit.
 19. The method of manufacturing thebase module of claim 18 wherein the test point connector comprises atemperature sensor and an electrical sensor.
 20. The method ofmanufacturing the base module of claim 18 further comprising configuringthe base module to receive a test accessory.
 21. The method ofmanufacturing the base module of claim 18 further comprising disposing aplurality of selectively moveable conductive contacts within thesubunit.
 22. The method of manufacturing the base module of claim 19further comprising configuring the test point connectors to conveyoperation conditions of the subunit when the conductive contacts arefully engaged with a supply bus.
 23. The method of manufacturing thebase module of claim 18 further comprising permanently integrating thebase module and the test accessory.
 24. The method of manufacturing thebase module of claim 19 further comprising forming lug terminals on theinternal components of the motor control center subunit to receive thetest point connectors.
 25. The method of manufacturing the base moduleof claim 18 further comprising outfitting the accessory with a shuttersystem to prevent unintentional operator contact with the signalsindicative of operation characteristics of the motor control centersubunit.